1. Field of the Invention
The present invention relates to an improved steering angle sensor arrangement structure used with a motor-driven power steering apparatus in a vehicle intended for rough road use. The motor-driven power steering apparatus uses an assist motor as a driving source for giving a steering mechanism a steering assist force. Also included is a power supply diagnostics device for supplying an electric power from a secondary battery and an alternator to an electric power load part.
2. Description of Background Art
Japanese Patent Laid-Open No. 2004-231011, for example, discloses a steering angle sensor arrangement structure of a vehicle intended for rough road use a type incorporating a potentiometer as a steering angle sensor for detecting a rotational angle of a steering shaft, or a steering angle, disposed in a gear case of a motor-driven power steering apparatus. As shown in FIG. 4 of Japanese Patent Laid-Open No. 2004-231011, a steering shaft 50 includes an upper side shaft 50a, a lower side shaft 50b, and a universal joint 51 for connecting together the upper side shaft 50a and the lower side shaft 50b. The steering shaft 50 is rotatably supported by an upper bracket 53 mounted in an upper pipe 18 and a lower bracket 54 mounted in a front cross pipe 23.
The lower side shaft 50b is a member that penetrates through a gear case 55 mounted in the lower bracket 54. The gear case 55 includes a potentiometer 61 for detecting a rotational angle and a rotational speed of the steering shaft 50.
Assume, for example, a situation, in which the potentiometer 61 becomes inoperative, requiring repair or replacement. If, in this case, the structure involved defies removal of the potentiometer 61 from the gear case 55, it becomes necessary to remove a whole motor-driven power steering apparatus from the upper pipe 18 and the front cross pipe 23, or to remove the lower bracket 54 from the front cross pipe 23 before removing the gear case 55. This makes maintenance of the potentiometer 61 troublesome and requires a large number of man-hours.
In addition, Japanese Patent Laid-Open No. 2002-316654, for example, discloses a motor-driven power steering apparatus using a steering angle sensor for detecting a turning angle of a steering shaft and controls an output torque (a steering assist force) of an assist motor by incorporating a value detected as the turning angle of the steering shaft.
The related art motor-driven power steering apparatus described above has the following disadvantages. Specifically, the conventional apparatus requires a steering angle sensor dedicated to the purpose and a control system as fail-safe means for the steering angle sensor. This has resulted in cost and weight being increased because of a complicated construction involved. Therefore, there is a demand for solving these problems.
Further, Japanese Patent Laid-Open No. 2000-206215, for example, discloses a power supply evaluation device for vehicles performing diagnostics of a battery, whether the battery is faulty or deteriorated, is based on a terminal voltage value and a discharge current value of the battery.
A battery is commonly said to be open if a battery voltage is weak or a battery terminal is disconnected, thus causing a voltage supplied from the battery to an electric part to be in short supply or interrupted. In such an open battery state, an electric power is supplied to each of the electric parts in a condition, in which a voltage from the battery is added to a voltage from an alternator, or in a form of only the voltage from the alternator. If a vehicle involved includes an electric power load part requiring relatively a large electric power, such as a motor-driven power steering or the like, the amount of electric power consumed for operating the part is excessively large, which is undesirable. There is a need for improving this drawback.